Recent data show that exposure of tissue culture cells to temperatures a few degrees above their normal physiological range leads to the rapid induction of a limited set of proteins. Synthesis of these few proteins can account for up to 40 per cent of the cell's protein synthetic capacity and some of the proteins accumulate to a level approaching 1 per cent of the cell's total protein. The major goals of this research program are to determine the function of these "heat-shock" proteins induced in primary cultures of chicken embryo fibroblasts (CEF) and to study, at the molecular level, the regulation of their synthesis. Three heat-shock proteins will be purified to homogeneity and antibodies prepared. These antibodies will be used to measure normal levels of the proteins in a variety of tissues and to measure effects on various enzymatic activities that may be involved in the heat-shock response. Results of these experiments should allow us to assign a function to the induced proteins. Study of the regulation of heat-shock protein synthesis will be initiated by employing recombinant DNA technology to prepare cDNA probes. Polyadenylated RNA will be isolated from polysomes of heat-shocked cells, partially purified, extrinsically labelled with radioactive isotopes, and used to isolate appropriate clones from the chicken cell recombinant DNA library carried in lambda phage. Specific cDNAs will be prepared by additional cloning procedures and these will be used to measure levels of heat-shock mRNAs during normal cell metabolism and during the induction and recovery from heat-shock. The response to heat shock provides an important model system for studying regulation of gene expression in eucaryotes as well as offering a tissue culture system for studying those metabolic activities that are used to protect cells from certain kinds of environmental stress such as hyperthermia.